The present invention relates to combinations of selected migrating corrosion inhibitors blended with concrete modifiers to produce novel products or formulations with dual functions for blending with raw concrete.
These novel products incorporate the feature of a concrete mix modifier and provide and/or enable a new method of adding migrating corrosion inhibitors into concrete at a stage where very efficient, synergistic, and long-term rebar corrosion control is achieved.
In an early published reference to the use of concrete modifiers they were described as water reducers. These reducers were typically polymers of condensed naphthalene sulfonic acids and were described in Industrial and Engineering Chemistry News in 1936. These sulfonated chemicals were never used on a large scale until the 1970""s when they were rediscovered for use as high range water reducers and called superplasticizers.
The main chemicals used in concrete as water reducing agents are the salts of lignosulfonic acids, the salts of hydroxycarboxylic acids, and carbohydrates. Superplasticizers (which are also water reducers) are broadly classified into four groups: sulfonated melamine-formaldelhyde condensate (SMF), sulfonated naphthalene-formaldehyde condensates (SNF), modified lignosulfonates (MLS) and blends of all these with other molecules.
The selected corrosion inhibitors useful for blending with superplasticizers are amino alcohols, amino silanes, amine salts, Ca(NO2)2, aminocarboxylates such as ammonium benzoate and the glucoheptonate salts as disclosed in U.S. Pat. No. 5,597,514, entitled xe2x80x9cCorrosion Inhibitor for Reducing Corrosion in Metallic Concrete Reinforcementsxe2x80x9d, and assigned to the same assignee as the present application.
We have found that a synergistic effect is achieved with the proper ratio and selection of retarder and corrosion inhibitor. We have found that use of a retarder which functions to reduce the bonds between silicate particles produces a much more liquid or fluid concrete mix than one at the same water content but without the retarder. It is believed that this feature facilitates migration of the corrosion inhibitor and provides a much higher level of rebar protection.
The examples were evaluated in three different test procedures designed to measure the effectiveness of corrosion inhibition in the presence of retarder chemicals.
Immersion testing was carried out with carbon steel panels about 1xe2x80x3xc3x974xe2x80x3 immersed in 3.5% NaCl solution for 168 hours. The corrosion inhibitor and retarder is added to the salt solution at a 2% level based on active ingredients. After 168 hours the panel is removed, wiped, the corrosion residue removed, and the weight loss due to corrosion determined. The control in the test data was immersed in 3.5% NaCl solution only.
The working electrode was a cleaned carbon standard rebar embedded in mortar which was prepared with a mixture of retarder and corrosion inhibitor added as an admixture. The specimens were cured for 28 days and then soaked for 20 hours in a 3% NaCl solution. Impedance spectra was obtained in the range of frequencies 106-10xe2x88x923 Hz The corrosion inhibitor retarder mixture was added to the concrete as suggested by the retarder suppliers. The ratio of inhibitor to retarder was 1 to 3.
Cyclic polarization curves were obtained by placing a carbon steel electrode in a solution of 3.5% NaCl plus 1.5% Ca(OH)2 which simulates the pore solution in Portland cement mortar. The curve is characterized by scanning the potential from the slightly cathodic area through the potential in the anodic area until the current reaches a level of anodic current of 10xe2x88x923 a/cm2 and back. The corrosion inhibitor, retarder mixture was added to the 3.5% NaCl solution at a 2% level based on active ingredients. The immersion test (ASTM-G31-72) and the cyclic polarization test (ASTM-G5-87) demonstrate effective protection in a fluid state mode and the ASTM-G106-89 test demonstrate protection in the cured (28 days) concrete specimens.